1. Field of the Invention
The invention generally relates to diesel filter systems and fuel heating devices for use in such systems, and in particular to systems and heating devices comprising a PTC heating element and a heat conductor which is in thermal contact with a PTC heating element.
2. Description of the Related Art
Presently, diesel engines are equipped with highly developed injection mechanics requiring high quality filtration techniques for guaranteeing reliable operation of the diesel engine. Diesel filter systems used for this purpose may be arranged at any position between the fuel tank and the diesel engine. Besides, the lifetime of the diesel injection assembly is largely influenced by the quality of the fuel filter.
Diesel fuel filters of different constructional design are well known. Usually, the actual filter element consists of high-grade impregnated very fine special purpose filter paper, but it make likewise consist of felt. The diesel filter system serves first of all for removing water in the fuel to prevent damage of the engine and to avoid destructive acidification. Moreover, solid particles such as oxides, dirt and dust particles are filtered out of the fuel.
At low temperatures, it is necessary to apply a filter heating to liquefy the paraffin portion in the diesel fuel. Thereby the lubricity of the fuel is increased and cold starting diesel engines is facilitated. Furthermore, the processes of forming waxes and gels are impeded and the lifetime of the fuel filter is increased.
Many heating devices for diesel oil have been developed, which apply PTC heating elements. Such heating elements are equipped with cold conducting thermistors having a positive temperature coefficient (PTC). PTC resistors are usually made of ferroelectrical ceramic semiconductor material in the form of rods, disks or pellets on the basis of barium titanate and metal oxides or salts. Because of the positive temperature coefficient within a certain temperature range, PTC thermistors are suitable in particular for temperature controls.
A diesel heating device using PTC elements is for instance known from EP 0 162 939 B1. This heating device is an integral part of a fuel filter consisting of a housing in which a filter cartridge is put into a removable base. The PTC elements are formed having a central hole and are positioned and fixed together with contact plates at locking pins of the housing. Such a heating device therefore requires a specifically constructed arrangement in the fuel filter.
The present invention has been made in consideration of the above-situation and has as its primary object to provide a diesel filter system and fuel heating device having enhanced installation capabilities.
It is another object of the present invention to increase heat transfer from the PTC heating element to the fuel.
A further object of the present invention is to allow for a higher rate of flow in combination with a compact arrangement of the diesel filter system and fuel heating device.
It is still another object of the present invention to provide a diesel filter system and fuel heating device specifically designed for applications in trucks and large emergency power plants.
Another object of the present invention is to provide a fuel heating device which is capable of being incorporated into different diesel filter systems without high constructional efforts.
Furthermore, it is an object of the present invention to provide a heating device which can be used as a supplementary accessory system.
These and other objects of the present invention will become apparent hereinafter.
To achieve these objects, the present invention provides a diesel filter system comprising filter means and fuel heating means. Said fuel heating means comprises a PTC heating element and a rod-shaped heat conductor being in thermal contact with the PTC heating element. The rod-shaped heat conductor comprises at least two tubular parts arranged in parallel. The PTC heating element is located between said at least two tubular parts.
According to a second aspect, the invention provides a fuel heating device for use with diesel filter systems. The device comprises a PTC heating element and a rod-shaped heat conductor being in thermal contact with the PTC heating element. The rod-shaped heat conductor comprises at least two tubular parts arranged in parallel. The PTC heating element is located between said at least two tubular parts.
By means of said two tubular parts arranged in parallel in the heat conductor, an axial passage of the fuel is achieved. This leads to an improved fuel guiding. Due to the tubular construction of the heat conductor, there is an opening required for the installation of the heating device according to the present invention of only such a kind that may be advantageously made for instance by drilling. It is then possible to seal the fuel heating device in a simple manner by means of an O-ring.
Since the PTC heating element is positioned between both parts of the heat conductor, the heat transfer is advantageously improved, leading to a higher rate of flow in combination with a compact constructional design. The heat conductor may be formed of sheet metal which reduces significantly the fabrication costs. Further, the heat conductor may advantageously be equipped with a perforated outer wall thereby allowing for a transversal flow additionally to the axial fuel passage. This transversal flow again improves the heat transfer to the fuel, thereby again allowing for increasing the rate of flow.
Further, the PTC heating element and the heat conductor may be held in a rod-shaped heater housing, thereby increasing the mechanical stability of the heating device. In order to reduce the rate, the heater housing may be made of plastics. For allowing simple assembly and disassembly of the heating device, the heater housing may further be equipped with a housing base part. Further, for giving the system the capability of automatically switching on and off, a temperature switch may be put into the housing.
Finally, the PTC heating element may be formed by a plurality of thermistors. This compensates for device tolerances and increases the reliability of the heating device.